Although childhood obesity is a common problem, few studies have evaluated the pulmonary complications of obesity in the pediatric population. We performed pulmonary function tests (PFT's), polysomnography and multiple sleep latency tests (MSLT's) in 22 obese children and adolescents (10 + 5 [SD] years; 184 + 36% ideal body weight), none of whom presented because of sleep or respiratory complaints. PFT's were normal in all but 2 subjects. Ten (46%) subjects had abnormal polysomnograms. There was a correlation between the degree of obesity and the apnea index (r=0.47, P < 0.05), and an inverse correlation between the degree of obesity and the SaO2 nadir (r= -0.60, P < 0.01). The degree of sleepiness on MSLT correlated with the degree of obesity (r = - 0.50, P < 0.05). We conclude that obese children and adolescents have a high prevalence of sleep-disordered breathing. We recommend that pediatricians have a high index of suspicion for OSAS when evaluating obese patients, and that polysomnography be considered for these patients.